This invention relates to an air conditioning system using a mixture of three types of refrigerants as a substitute for Freon.
The basic components of an air conditioning system 1 of the type currently in use will be described with reference to FIGS. 4 and 5.
The components of the air conditioning system 1 include a compressor 2, a four-way valve 3, an outdoor heat exchanger 4, an expansion valve 5, an indoor heat exchanger 6 and an accumulator 7. These components are provided in a refrigerating circuit. The accumulator 7 is for accumulating part of the refrigerant included in a low-temperature, low-pressure vapor-liquid present in a low-pressure line downstream of the expansion valve 5 immediately after start-up. The accumulator 7 makes it possible to prevent part of the refrigerant from being drawn into the compressor immediately after start-up.
In the cooling cycle, which is illustrated in FIG. 4, high-temperature, high-pressure gas is supplied from the compressor 2 to the outdoor heat exchanger 4, which serves as a condenser, via the four-way valve 3. The gas is condensed in the outdoor heat exchanger 4. The condensed phases are rendered into two phases, namely low-temperature, low-pressure gaseous and liquid phases, by the expansion valve 5. The result is supplied to the indoor heat exchanger 6, which serves as an evaporator, where evaporation takes place to produce a low-temperature, low-pressure gas. As a result, heat is absorbed from the interior of the room, thereby cooling the room. Finally, the low-temperature, low-pressure gas is returned to the compressor via the accumulator 7. Cooling of the interior of the room is carried out by repeating the cooling cycle described above.
In the heating cycle, which is illustrated in FIG. 5, high-temperature, high-pressure gas is supplied from the compressor 2 to the indoor heat exchanger 6, which serves as a condenser, via the four-way valve 3. The gas is condensed and converted to a high-temperature, high-pressure liquid in the indoor heat exchanger 6. As a result, heat is released into the room to warm the room. The high-temperature, high-pressure liquid is rendered into two phases, namely low-temperature, low-pressure gaseous and liquid phases, by the expansion valve 5. The result is supplied to the outdoor heat exchanger 4, which serves as an evaporator, where evaporation takes place to produce a low-temperature, low-pressure gas. The low-temperature, low-pressure gas is returned to the compressor 2 via the accumulator 7. Heating of the interior of the room is carried out by repeating the heating cycle described above.
Heretofore these cycles of the air conditioner have been implemented using Freon gas as the refrigerant. However, the use of Freon gas is now banned by reason of the fact that Freon causes global warming due to destruction of the ozone layer. Table 1 illustrates the specific types of Freon gas whose use is prohibited.
TABLE 1 ______________________________________ Tb (Boiling Point Under Atmospheric Symbol Component Pressure ______________________________________ CFC-11 CCl.sub.3 F 23.7.degree. C. CFC-12 CCl.sub.2 F.sub.2 -29.8.degree. C. CFC-113 CClF.sub.2 -CCl.sub.2 F 47.6.degree. C. CFC-114 CClF.sub.2 -CClF.sub.2 3.6.degree. C. CFC-115 CClF.sub.2 -CF.sub.3 -39.1.degree. C. ______________________________________
Much research has been conducted into gases which are substituted for Freon gas. New refrigerants have been developed upon taking into consideration that the refrigerant have characteristics that resemble those of Freon gas, that the refrigerant exhibit a Trb (critical temperature) at which vapor will not liquefy at a low Tb (boiling point under atmospheric pressure) and at high compression, and that the refrigerant having a high coefficient of performance and a high efficiency. [When the influential physical properties are ranked, we have the following: Cp (specific heat)&gt;Tb (boiling point at atmospheric pressure)&gt;Trb (critical temperature)&gt;Pc (critical pressure)&gt;Zc (critical compression coefficient).] The use of a mixed medium has become the focus of attention because Tb can be selected at will and because it is possible to improve upon drawbacks encountered in terms of the thermodynamic characteristics, solubility and combustion characteristics of the medium.
Mixed media can be classified into an azeotropic mixed medium and a non-azeotropic mixed medium. In an azeotropic mixed medium, the compositions of the gaseous and liquid phases do not change at the boiling point (which corresponds to Tb), and therefore the mixed medium behaves in the same manner as a single medium. An advantage of such mixed media is that the techniques and facilities established for a single medium can be utilized without modification. With a non-azeotropic mixed medium, on the other hand, the dew-point curve (cohesion curve) and boiling-point curve are separate over the entire composition range and therefore the compositions of the gaseous phase and liquid phase differ. The liquid phase is always rich in high-Tb media.
A mixed medium proposed thus far contains two or three components. An example of a two-component system is HCFC-22 (CHClF2; Tb -40.8.degree. C.) 45% and HCFC-142b (CH3CClF2; Tb -9.2.degree. C.) 55%. However, such a mixed system has little practicality since it is dangerously combustible.
A patent relating to a mixed medium having three or more components disclosed by Dupont in January of 1989 skillfully mixes components having different values of Tb and combustibility to realize a behavior approximating that of an azeotropic mixed medium in practical terms. Three typical components are HCFC-22, HFC 152a (CHF.sub.2 CH.sub.3 ; Tb -24.15.degree. C.) and CFC-114 (CClF.sub.2 CClF.sub.2 ; Tb -3.8.degree. C.) or HCFC-124 (CHClFCF3; Tb -12.degree. C.). These are mixed at a weight ratio of 36:24:40, respectively, and the mixture is used as a medium for air conditioning.
With the above-described mixed medium as a background, the present invention uses the mixed medium of Table 2 below in an air conditioner.
TABLE 2 ______________________________________ Chemical Proportion by Symbol Component Tb (.degree.C.) Weight (wt- %) ______________________________________ R-32 CH.sub.2 F.sub.2 -52.8 23 (or 30) R-125 CHF.sub.2 CF.sub.3 -48.6 24 (or 10) R-134a CH.sub.2 FCF.sub.3 -26.2 52 (or 60) ______________________________________
The mixed medium shown in Table 2 uses R-134a instead of CFC-12, which is one of the specified Freon gases. The shortcomings that accompany use of R-134a, namely a decline in the refrigerant performance, diminished power from consumption and a reduction in weight flow rate, are compensated for by the addition of R-32 and R-125, which have a low Tb. Though this is not an azeotropic system, circulation of the low-Tb components is possible.
A first object of the present invention is to provide an air conditioner in which, by fully exploiting the characteristics of a mixed medium comprising the three components of R-32, R-125 and R-134a, namely by focusing upon the different boiling points of these components, it is possible to increase the gas components of R32 and R125 when the load on the air conditioner increases.
When a mixed medium comprising the three components of R-32, R-125 and R-134a is passed through the condenser of an air conditioning system which includes a refrigerator, the R-134a having the high boiling point is condensed at an early time. Two phases, namely a liquid phase rich in R-134a and a gaseous phase rich in R-32 and R-125, are produced in the piping of the condenser, as a result of which the efficiency of thermal transfer within the piping and radiation of heat from the piping walls declines. The increase in the gaseous phase reduces flow velocity through the piping and lowers the efficiency of condensation.
A second object of the present invention is to provide an air conditioner heat exchanger which solves these problems encountered in the prior art.
According to the present invention, the first object is attained by providing an air conditioner having a circuit connecting a compressor, a four-way valve, an outdoor heat exchanger, an expansion valve, an indoor heat exchanger and an accumulator, wherein a mixed medium of R-32, R-125 and R-134a is sealed within the circuit, a supercooled heat exchanger and a liquid-gas tank are arranged between the outdoor heat exchanger and the expansion valve and the liquid-gas tank is connected to the accumulator via a valve.
Owing to the difference in the boiling points of the three components constituting the mixed medium, R-32 and R-125 vaporize rapidly when the liquid phase is returned to the accumulator. This makes it possible for the compressor to draw in a large amount of the gaseous components. As a result, the compressor is capable of following up a change in load rapidly and efficiently.
According to the present invention, the second object is attained by providing a heat exchanger for an air conditioner which includes a refrigerator, arranged between a compressor and an expansion valve, for condensing a three-component mixed medium, the heat exchanger comprising a first condenser connected to the compressor, a liquid-gas separator connected to the first condenser, a second condenser for receiving a gaseous component within the liquid-gas separator, and a supercooled heat exchanger connected to a discharge port of the second condenser and an intake port of the expansion valve, a liquid component within the liquid-gas separator being supplied to an intake port of the supercooled heat exchanger.
Further, according to the present invention, the second object is attained by providing a heat exchanger for an air conditioner which includes a refrigerator, arranged between a compressor and an expansion valve, for condensing a three-component mixed medium, the heat exchanger comprising a first condenser connected to the compressor, a liquid-gas separator connected to the first condenser, and a second condenser for receiving a gaseous component within the liquid-gas separator, a liquid component within the liquid-gas separator being supplied to an intake side of the expansion valve.
In a preferred embodiment, the first condenser has piping diameter greater than that of the second condenser and the three-component mixed medium comprises R-32, R-125 and R-134a.
In operation, the liquid phase along the piping of the condensers is drawn off, the flow speed of high-pressure gas from the compressor is raised and the high-pressure liquid is compressed in the remaining portion of the piping. This makes it possible to improve the rate of contact heat transfer between the high-pressure liquid and the piping.